This invention relates in general to methods and apparatuses for gathering and interpreting data regarding the amount of roughness that is present on a surface of an article. In particular, this invention relates to an improved method and apparatus for measuring, analyzing, and characterizing irregularities that are present on the outer surface of an article for the purpose of generating better quality information for various engineering and other uses.
A wide variety of mechanical structures are known in the art that employ two or more components that abut or otherwise engage one another in some manner during use. For example, annular seal assemblies are well known structures that include a flexible sealing element that slidably engages an outer surface of a rotatable shaft so as to prevent a fluid (such as oil) from passing therethrough when the shaft is rotated during use. Bearings are also well known structures that include one or more bearing elements, such as cylindrical roller bearings, that slidably or rotatably engage an outer surface of a rotatable member. Also, gears are well known structures that include respectively pluralities of teeth that mesh with one another to effect concurrent rotation.
In each of these and in other mechanical structures, the outer surfaces of the components engage and cooperate with one another in some manner during use. In many instances, the relative smoothness or roughness of either or both of the outer surfaces of the components can be very important in determining whether the mechanical structure will function efficiently or, in some cases, function at all. For example, in an annular seal assembly, it has been found desirable for the outer circumferential surface of the rotatable shaft to have a variety of relatively small irregularities formed therein. The presence of some of such irregularities has been found to be desirable because they provide small recesses that can retain fluid therein, which functions as a lubricant to minimize the adverse effects of friction and heat that would otherwise be generated at the sealing element when the shaft is rotated during use. So long as the irregularities are relatively small in size and sufficiently randomly distributed over the outer circumferential surface of the shaft, then their presence will not likely affect the operation of the annular seal assembly. In other mechanical structures, however, it may be desirable to have a different surface configuration for the components that engage one another. The particular surface configuration for such components will vary from application to application in accordance with many factors, including material composition, manner of engagement, load magnitude, and other engineering considerations.
Unfortunately, the size and orientation of the irregularities formed in the outer surfaces of the components are so small as to be not visible to the naked eye or otherwise readily ascertainable. To overcome this, a variety of devices have been developed that can gather raw data regarding the relative smoothness or roughness of the surface of an article. Many of these devices are capable of presenting the gathered raw data in either a qualitative format (such as in a visual two-dimensional or three-dimensional representation) or in a quantitative format (such as in a mathematical representation). Although interesting in some instances and for some purposes, the usefulness of these qualitative and quantitative representations of the raw data is somewhat limited.
To improve the characterization of the surface of an article, it is known to initially measure the size and orientation of the irregularities formed therein, then to perform one or more mathematical operations to derive a parameter that is indicative of such irregularities. A variety of roughness parameters have been established over the years. For example, an arithmetic average roughness parameter (commonly referred to as Ra) and a root mean square roughness parameter (commonly referred to as Rq) are well known in the art. However, it has been found that these and other parameters that are known in the art do not provide a sufficient amount of information to be useful in certain engineering and other uses. Specifically, it has been found that these and other known parameters cannot, at least in some instances, sufficiently characterize the surface of the article so as to clearly distinguish between differing surface textures that can adversely affect the operation of the mechanical structure. Thus, it would be desirable to provide an improved method and apparatus for measuring, analyzing, and characterizing irregularities that are present on the outer surface of an article for the purpose of generating better quality information for various engineering and other uses.